Heinrich,

  I get that the Marples rig is balanced, and for a boat that needs to sail in both directions, that's a serious benefit (Rick's neat trick of sailing with the ww hull to leeward, in order to balance out the forces, notwithstanding).

  However, I never quite understood how the Marples rig would make it easier to safely reduce sail area.  It also seems to have some other limitations as well.

  Here's what I don't get about the Marples rig (feel free to correct me if I'm not seeing something):

  - EASE OF USE.  It appears that the reefing mechanism would end up being more complex than a furling boom, requiring some serious hardware (or computer control) to keep the bottom and top of the center torsion furler synchronized with the two outhauls.  I don't see how that would be easier than a furling boom with a solid internal mandrel and a single halyard. 

     It's even possible that a junk rig might actually be easier to reef than either the Marples or the furling boom.  Annie Hill makes it sound pretty effortless when writing about the junk rig she used on Badger and Fantail.  (well, unless you had a motorized furler, which is what Marples mentions, and I imagine is as easy as it gets)

  - JAMMING.  If a furling boom jams, at least you can take the sail down by hand.  Slab reefing or a junk rig would be even more fault-tolerant.  The worst case is having to go aloft to cut a halyard, and granted, that's not cool.  But the Marples rig needs to have all four corners working on concert.  If any of the pieces stop working during a big blow, you could be in a world of hurt, and solving the problem could be a lot worse than cutting a single halyard.

  - SHUNTING.  Something this complex would scare me (of course, I'm easily scared) when shunting a larger boat in a big wind.  Unless you furl it in before the shunt, that's a lot of sail area that has to take the full force of the wind, even if briefly.  The dynarig worries me for the same reason, but this has the added complexity of that reefing mechanism.

  - DEPOWERING.  With good una, schooner, or junk rig, you can depower the sail and leave it unattended for a while by uncleating the mainsheet.  I don't see how the Marples rig would give you that same benefit.  If you have a crew, or a computer, that's probably not an issue most of the time.  But if something happens and the crew or computer aren't working, this could be a problem.

  - WEIGHT ALOFT.  Wouldn't the diamond rig have more weight up high?  That horizontal spar can't be a weak thing, and that joint would have to be pretty beefy to support point loads at the ends of those spars when the full sail is up.  That beef has to way something, and that weight is not down by the deck.

  - WINDAGE AT ANCHOR.  That cross piece looks like it would catch a lot of air when anchored in a blow.  You could put a vane on the back to feather it, but I think that might invite harmonic oscillations in bigger winds.

  - SAIL SHAPE.  Unless you have a semi-rigid "luff" down the center of the torsion furler, such as with a CDI flexible furler, it's not going to furl evenly in a good wind, and/or the center will pull out as the sail gets stretched.  Kind of like trying to furl a reacher with a vectran self-furling luff -- in works, out works, halfway out gets a bit weird.  It might work on a model or a dinghy, but there would be a *lot* of force on that furler for a 40' - 60' boat.  The Marples rig would be better than the  self-furling reacher because you'd theoretically be twisting the bottom and top at the same rate, but the center would still pull out.  That might not be good in big, gusty winds.  And if you did have a semi rigid luff, I'm not sure the sail would maintain its nice full shape.

---

  Like the Hoyt rig, I think the Marples rig is a very good idea, and an innovative response to complex needs.  But it might be challenged when scaled up for a larger boat in big weather.

  Please note: if you're a big fan of the Marples rig, I'm not going to try to convince you that you're wrong.  The more rigs people put on proas, the more we learn. 

  I'm just still searching for the perfect rig, for my personal criteria, and am having trouble latching on to the Marples.  I'm happy to be convinced.  Or if I still don't get it, I'm happy to be among the ignorant.

        - Mike

  



heinrich_meurer wrote:

 

Also four wingtip vortices instead of one - so less performance orientated but certainly easy to reduce sail area and therefor safe.

Heinrich

--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
>
> Great to have a play with. My concerns are that a) triangular tips are
> pretty useless, b) the leading edges are not rigid enough so will sag, and
> c) the draft will be pushed aft. Maybe. Give it a go and let us know how
> it works. Should be easy enough to step it in the same hole as a
> conventional rig, so no big deal to swap if it doesn't work as well as you
> would like.
>
> How big a boat do you want? A flat panel elementarry is quite capable of
> beating the Nacras if the rig is big enough. If the diamond rig does not
> perform well enough, then the schooner rig we originally used on the boat
> will be pretty quick, if you have a crew. Hard work solo, when a taller
> una rig would be the answer. Next step up is the Wooden Boat Design
> Challenge boat which is a fair bit longer, but would be a lot quicker.
>
> I would build it the same way you want to build the big boat. Maybe put
> the same rig on it as well to learn how it works. Beat the nacras and
> resale might be better than you expect.
>
> Any questions, let me know.
> regards,
>
> rob
>
> On Tue, Feb 7, 2012 at 11:28 AM, sfbaysailingdad <mitch.sailing@...>wrote:
>
> > **
> >
> >
> > Hi Rob,
> >
> > I might be willing to give this a go - I'm selling my Contour 34 tri with
> > the likelihood of getting something quite big, and in the interim would
> > like to try to give some of the hot local catamarans some fits.
> >
> > Brief would be in the bay point to point racing, not much windward/leeward
> > stuff.
> >
> > Thoughts? John Marples is local, so assuming I can get to the platform
> > stage, he'd likely willing to test out his new sail plan.
> >
> > I do assume little in resale - so this would have to be an inexpensive
> > build. I wouldn't mind stressed ply, or foam/glass. No need for carbon,
> > unless maybe the beams…
> >
> > Greg
> >
> >
> >
>

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